JazzEars
There may be other ways, but here is code that I found.
Your list box will be a simple Multi-Select list box. Put a check box on your form. Checking it will select all records, unchecking it will deselect all.
Dim i As Integer
If Yourchkbox Then
For i = 0 To Yourlistbox.ListCount - 1
Yourlistbox.Selected(i) = True
Next i
Else
For i = 0 To Yourlistbox.ListCount - 1
Yourlistbox.Selected(i) = False
Next i
End If
Change Yourchkbox to the name of your check box. Change Yourlistbox to the name of your list box.
Put the code on the Click event for Yourchkbox.
Tom